There are many known devices designed to attract and capture and/or kill insects. Devices for trapping insects for research purposes are typically referred to as "traps", while devices that also kill the insects have various names, including the PG,3 colloquial terms "bug killer" and "bug zapper". The motivation for the latter devices is generally to destroy insects that are pests to humans, such as members of the Anopheles and Aedes species of mosquitoes, which are both known to be disease carriers.
Entomological research suggests that members of various species of mosquitoes are attracted to light in various wavelengths. It is well known that light attracts many types of insects, including mosquitoes, so most of the prior devices include a light source as an attractant or lure. Such devices sometimes take advantage of the discovery that some species of mosquitoes are attracted to light in a range of ultraviolet (UV) wavelengths, and possibly certain infrared wavelengths. Fluorescent lights, sometimes with special phosphors to enhance the ultraviolet spectral content of the emitted light, are often used as the light source, but some older devices relied upon incandescent bulbs.
Some prior art light-attractant devices also included a fan, with the fan typically designed to establish a sufficiently large air current such that any insect that approaches the light lure closely to the air intake will be irretrievably caught in the air flow and pulled into the device. Thus, some prior art devices included a light as an attractant, a fan to pull insects into the device, and either a trap for holding the insects, an electric grid to kill the insects, or simply a plate to kill them on impact, for example, see U.S. Pat. Nos. 2,806,321, 3,041,773 and 3,152,420. U.S. Pat. No. 4,908,978 discloses a device that includes a fan and an electric grid, but has no light or other attractant.
Various types of insect traps, such as the New Jersey trap, the CDC trap, the Nozawa trap, etc., have been used by researchers to capture different species of mosquitoes and preserve the catch for research purposes. Many of these traps have light lures and are thus considered "light traps." Common designs include a light source positioned over a vertically disposed air intake, a screen to exclude larger insects, a fan to draw air down into the air intake, a collection bottle or bag, and a flat, concave, or conical metal or plastic cover placed above the trap to protect it from rain. Variations of the design include downwardly facing openings for bottom draft intake, since research suggests that updraft-type traps may be more effective in some instances than downdraft types.
Other prior art devices do not include a fan, and depend solely on the light to attract the insects and draw them in. The currently popular commercial "backyard" insect electrocution devices use an electric grid to kill insects but do not include a fan. The most common arrangement is to provide a light source for attracting insects (typically UV) and spaced apart electric current-carrying grids surrounding the light source. Insects attempt to reach the light source and are killed by the electrified grids, which are typically spaced such that smaller insects cannot avoid touching or coming within operative proximity of the electrodes if they approach the light lure.
Many UV-lure electrocution devices are touted as being able to clear an area of mosquitoes up to a certain number of square feet or acres. Curiously, however, research has shown that these UV-lure devices are ineffective to reduce mosquito biting. The research suggests that such devices actually increase the count of biting female mosquitoes within the general vicinity of the device. The overall effect of the device may be to attract more biting insects to an area having an UV-lure device than an area without such a device. Some of the increased biting population will be electrocuted, but many will be diverted by the more compelling lure of human bait in the area. Since humans are known to be more attractive to mosquitoes than UV lures, the research suggests an increased bite rate for yards having a conventional UV-lure electrocution device than yards without them.
Further research suggests that mosquitoes have a reflexive defensive reaction to the detection of minute changes in air flow velocity and/or direction. Upon encountering a change in air flow velocity and/or direction, such as is produced in the vicinity of insect traps and electrocution devices having fans, mosquitoes react by vigorous flight activity, with a strong lift component, ostensibly in an effort to avoid entrainment. Since mosquitoes are known to have extremely sensitive senses for warm blooded food sources, it may be expected that their sense for air currents is also very sensitive. It is possible that mosquitoes actually can avoid being pulled into conventional traps and electrocution devices having fans, by sensing the changes in air flow velocity and/or direction prior to being captured in a strong air flow. Therefore, areas utilizing such traps or devices may have a higher concentration of biting insects than areas without them.
Research also suggests that if a trap is of a conventional downdraft type with a fan, its air stream must overcome the lift factor in the mosquito's flight in order to capture the insect. If the trap creates an upward moving air stream, however, a mosquito's upward flight reaction contributes not to its escape, but to capture. Thus, some insect trap designs include a downwardly facing opening for a fan air intake, for creating an updraft.
In experiments involving comparisons between updraft and downdraft-type type traps, it was believed that the sustained captures by an updraft and the lowered catches of a downdraft trap when the air flow rates were reduced confirms the upward flight reaction by a mosquito to air movement. However, it was also observed that insects that managed to avoid being drawn into the trap characteristically escaped by flying upward and collected under the trap's rain cover, where they made continual attempts to fly higher. Accordingly, insect traps having rain covers positioned over an upwardly facing air intake tend to accumulate uncaught insects under the cover.
Other drawbacks to conventional UV-lure electrocution devices include the indiscriminate killing of nonpestiferous insect species. Species of insects which are "strong fliers" or those which have high body masses fly fast towards a lure and are unable to stop before encountering the electric grid. Beetles, by way of example, will be killed by electrocution devices, but beetles are not particularly dangerous pests to people.
Moreover, most electrocution devices tend to be noisy and aesthetically unappealing to many people. Many people believe that the crackling and sizzling sound that accompanies the electrocution of an insect is an indication of its effectiveness. However, a recent study showed that the vast majority (over 90%) of the insects killed by electrocution devices were not mosquitoes, with only about 3% being female mosquitoes. Other people find the noise from the device quite unappetizing.
Accordingly, there is a need for an insect killer that is relatively quiet, aesthetically appealing, and effective to attract, capture, and kill species of insects that are harmful to people, especially species of mosquitoes.